Abstract

The objective of this study was to evaluate the soil organic carbon fractions and the carbon management index (CMI) in a cohesive oxisol under different uses. Conventional cassava planting (CC), pasture (PP), and 7- and 12-year agroforestry systems (AF7 and AF12, respectively), were tested against secondary forest (SF). Soil samples of these areas were physically fractionated in order to determine total organic matter (TOC) as well as the labile- (LOC) and non-labile (NOC) fractions of the soil organic matter, as well as carbon management index (CMI). Total organic C ranged from 14.17 to 27.20 g kg^-1 of soil, showing no differences in the surface layer among the land uses as compared to the secondary forest. No differences were found in the surface layer for LOC as well, except for the AF12 where LOC was higher. This condition accounts for higher microbial activity and nutrient cycling in the soil. This system also showed higher CMI values, pointing to a better response of soil quality under long-term agroforestry system. This system improved soil organic matter, regardless of the depth. On the other hand, conventional cassava and planted pasture systems reduced carbon in soil. In conclusion, the agroforestry system is the best choice of farmers, when they seek for better soil quality.

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